This invention relates to improved biocompatible polymer compositions. Polymers of fluorinated monomers and alkyl acrylates demonstrate improved performance as coatings for implantable devices. Such coatings may, for example, be used to release a bioactive agent from the medical device. One specific application lies in drug eluting coatings for stents. Although stents have important medical uses, problems of restenosis and thrombosis remain. Pharmacological therapy in the form of a drug-delivery stent appears a feasible means to tackle these biologically derived issues. Polymeric coatings placed onto the stent serve to act both as the drug reservoir, and to control the release of the drug. The nature of the coating polymers plays an important role in defining the surface properties of a coating. For example, a very low Tg, amorphous coating material can have unacceptable Theological behavior upon mechanical perturbation such as crimping, balloon expansion, etc. On the other hand, a high Tg, or highly crystalline coating material introduces brittle fracture in the high strain areas of the stent pattern.
Some of the currently used polymeric materials such as poly(vinylidene difluoride-co-hexafluoropropene) (PVDF-co-HFP) have good mechanical properties, and acceptable biocompatibility, but also have low permeability to drugs. While PVDF polymers possess excellent characteristics that permit their use in medical device based coatings or articles, one aspect of PVDF polymer that could be a detriment is the low coefficient of surface friction. This is an intrinsic property of the polymer surface. This property could cause problems during stent securement process. Compositions within this disclosure aim at reducing the surface slipperiness or increase the surface friction so coated devices could be handled better. Use of hydrophobic acrylate or methacrylate based copolymer segments with glass transition temperature Tg below −35° C. could be elastomeric and could impart slightly higher friction.
In U.S. 2004/0224001, Pacetti, et al. disclosed a medical implant coating that includes a mixture of a hydrophobic polymer and a polymeric hydrophilic additive, wherein the hydrophobic polymer and the hydrophilic additive form a physically entangled or interpenetrating system. Pacetti, U.S. Pat. No. 7,244,443, and Ding, U.S. 2006/0067908, attempted to address some of the problems in this area through the use of a polymer formed of fluorinated monomers and hydrophilic monomers. The fluorinated monomers were said to provide mechanical strength and/or flexibility, biocompatibility, and physiologic durability for the polymer. Strickler et al., U.S. 2007/0117925, discloses copolymers having at least one fluorocarbon-containing block copolymer, which, in turn, contains (a) at least one fluorocarbon-containing, low glass transition temperature (low Tg) copolymer chain and (b) at least one glass transition temperature (high Tg) polymer chain. Other similar efforts include U.S. Pat. Nos. 7,175,873; and 7,247,313 to Roorda, et al.; U.S. 2005/0106204 to Hossainy et al.
The present invention is a further improvement by addressing the continuing problems in the art by providing a polymeric material for coating implantable devices.